As is well known in the art, microwave ovens must have door seals that substantially prevent the leakage of microwave energy so as to provide a safe environment for operators and to comply with government standards. There are many types of door seals in use today in domestic microwave ovens. However, the technological advances in domestic door seals do not satisfy all of the design requirements which may be presented by a large industrial batch type door seal. For example, it may be preferable that an industrial door open and close readily occupying a minimum of floor space. Also, it may be preferable that the choke structure of the door be of a noncontacting type so as not to be dependent on metal cleanliness or conductivity. Furthermore, it was always desirable to fabricate the door seal as inexpensively as possible such as using relatively light weight sheet metal and conventional sheet metal techniques.
More specifically, many microwave oven seals, both domestic and industrial, employ what has been referred to as a quarter wavelength choking principle. Generally, that is a choke structure whereby there is a one-quarter wavelength electromagnetic path from a gap between the choking surfaces, which path provides a high series reactance at the choke opening and reflects a short circuit from a terminating wall surface at the end of the path to energy directed through the gap. The separation of the choking surfaces at the gap is a critical distance in the performance of the choke. The distance must be large enough so as to prevent arcing between the surfaces but small enough so as to provide effective sealing. A thin layer of a dielectric material over one of the choking surfaces may substantially eliminate the arcing problem. With domestic oven seals, the doors and their frames are generally small enough so that both may be rigidly fabricated so that the distance between them is minimized. However, with large industrial batch type microwave ovens having doors a meter or more wide, it has been found most difficult and expensive to fabricate a rigid door and frame which has a minimum spacing around the periphery.